Linux Use Rocketing at Jet Propulsion Laboratories

A look at how JPL scientists are using Linux to build better spacecraft and make accurate calculations.

Few technologies are more exacting than
that of designing and running space probes. A trajectory error as
small as one inch per mile, for instance, can result in missing the
target by tens of thousands of miles. Now add stringent budgetary
constraints, and you have some idea of the daily working
environment of the scientists and engineers at the Jet Propulsion
Laboratories (JPL) in Pasadena, California.

Linux at NASA

With their long history of mainframe-based computing, NASA
scientists were quick to spot the benefits of Linux. The NASA
Goddard Space Flight Center, for example, uses Linux with its
airborne Scanning Radar Altimeter to study hurricanes. NASA's
Beowulf-class clustered computing project has also made use of
Linux for several years. Further, one NASA employee maintains a
site on the use of Linux for x-ray astronomers, and another is
harnessing it for the on-board navigational computers of space
probes. It's no surprise, therefore, that NASA's JPL is now
utilizing Linux in two very different projects: one to build better
spacecraft and the other to see that they arrive at the right
place.

Building Better Spacecraft

When you are two billion miles from earth, you can't just pop
out to a hardware store to get a spare part. JPL's Advanced Thermal
and Structural Technology Group (ATSTG), therefore, is responsible
for ensuring all space probe components can withstand the rigors of
space travel. The ATSTG works on advanced technologies for thermal,
cryogenic and structural space systems including aerobots, rovers,
mechanical coolers and heat pipes. They have recently integrated
Linux into the business of building better spacecraft.

Thermal engineers play a key role in the design of space
hardware. “Thermal engineering provides designs that maintain the
required temperatures at specific space hardware sites through the
range of all modes of operation and for the life of the hardware in
space,” says Technical Group Leader Jose Rodriquez. “Temperature
requirements for electronics, mechanisms, detectors and lasers are
critical to mission success.”

The ATSTG uses a number of analysis tools to develop
analytical models to carry out design trade studies. The best,
cheapest and most complete integrated thermal analysis package
available is the Thermal Synthesis System (TSS). It allows thermal
engineers to create a thermal model of the hardware in a simulated
space environment. They can then achieve a better understanding of
how well the system will actually work when it is out in space. At
the time it was developed, the TSS graphical interface requirements
could be met with only high-end HP machines running UNIX. When the
ATSTG wanted a version for its own use, the only free versions of
the software available were for HP running UNIX or Linux on a PC.
Given the choice between spending many thousands of dollars to buy
or rent an HP, or spending $150 US to buy Red Hat Linux and
Accelerated X, they opted for the Linux version of TSS. The group
also installed Linux TSS on computers at two subcontractor
facilities.

TCP/IP is used to transmit data and models back and forth
between Linux and Windows computers. “Because of the high expense
associated with the HP machines, it is necessary to keep them
utilized constantly to generate enough resources to pay for the
equipment,” states Rodriquez. “This is done by keeping as few
machines as possible, which means that engineers can't easily
access these computers during normal working hours and have to work
early or late hours to get the work done.” Having Linux allows the
ATSTG members to run TSS right on their own PC whenever they need
it, eliminating costly downtime and enabling projects to be
completed sooner.

The Right Place at the Right Time

Building a better spacecraft is fruitless, however, if it
never arrives at its intended destination. While some people have
trouble navigating their way across town, the scientists at JPL
have to plot a trajectory that will allow a space probe to
intercept a planet that is billions of miles away and traveling at
15,000 miles an hour. If you arrive a day late after a three-year
journey, you've missed the target by hundreds of thousands of
miles. As well as difficulties in hitting its space targets, there
are also budgetary targets that NASA personnel are expected to
meet. Linux is key to achieving both. “Smaller projects (DS1, Mars
Pathfinder, etc.) are trying very hard to cut costs while achieving
all scientific goals,” says Peter Breckheimer, Technical Group
Supervisor in the Navigation and Flight Mechanics Section of JPL's
Systems Division. “Computers to run the navigation system have
been very expensive in the past due to the high level of
performance required.”

Breckheimer's group has the responsibility of designing,
implementing delivering, and sustaining the Institutional
Navigation System Software (INSS) in all flight projects (Galileo,
Cassini, Mars, DS1, Stardust, etc.). Consisting of over 160
programs written primarily in Fortran 77 and C, Perl, Tcl/Tk and
HTML, INSS contains 4.5 million lines of source code. INSS is
designed to be readily portable to new platforms as they develop
(particularly Linux).

When JPL switched from mainframe to VAX in the eighties, it
required 15 man-years of software conversions. Later, for the move
to HP-UX, engineers used only standard features within the Fortran
77 and C compilers. As a result, portability issues are easy to
deal with. Going from HP-UX to Linux, therefore, took minimal work
and even tools like Perl and Tcl/Tk worked correctly the first
time. “There are tools we have experimented with to convert
c-shell to NT scripts, but we haven't been successful yet,”
reports Breckheimer. “As for Linux, no conversion was necessary.
The scripts worked properly with no changes.”

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